So-called electric vehicles such as electrical vehicles, hybrid vehicles or fuel cell vehicles are equipped with a power storage device made up of a secondary battery, a capacitor or the like, and generate driving force from electric power stored in the power storage device through a motor.
A configuration has been proposed in which the power storage device mounted on these electric vehicles is charged by an external power supply such as a system power supply or a solar cell. As for a hybrid vehicle, in particular, if the cost of charging by an external power supply is lower than that of electric power generation by a mounted engine, the overall driving cost can be suppressed by charging the power storage device by the external power supply.
The power storage device is often formed of a secondary battery utilizing the electrochemical action, and the charge/discharge characteristics thereof are significantly affected by temperature. Therefore, a configuration has been proposed in which a reduction in temperature of the power storage device is suppressed in the electric vehicle where the power storage device is configured to be rechargeable by the external power supply.
For example, Japanese Patent Laying-Open No. 08-214412 discloses a charge control apparatus for a power storage device for use on an electric vehicle including: a charging period calculating means for calculating a necessary charging period based on an amount of electric energy discharged from the power storage device for use on the electric vehicle when charging is commanded, a detected power supply voltage value and a predetermined charging current value; and a charging start time calculating means for calculating a charging start time to finish the charging at the indicated scheduled boarding time based on the indicated scheduled boarding time and the calculated necessary charging period. According to the invention disclosed in this Japanese Patent Laying-Open No. 08-214412, since the charging is finished at the scheduled boarding time, the period of time for which the power storage device is left to stand after it has been charged will be short, and any reduction in the capacity due to a temperature drop can be small.
In the electric vehicle put to practical use, however, it is also necessary to ensure not only the power storage device but also the passenger comfort. In other words, in winter, summer and the like, air-conditioning (heating or cooling) of a vehicle compartment space is required. This air-conditioning in the vehicle compartment requires a relatively large power source. Therefore, electric power to be used for generation of vehicle driving force is used for air-conditioning in the vehicle compartment, and the traveling performance may be restricted due to the power storage device. In other words, out of an amount of electric energy stored in the power storage device, an amount of electric energy that can be ensured for vehicle traveling may be decreased, and the distance that can be traveled may be shortened. Furthermore, out of electric power that can be discharged from the power storage device, electric power that can be ensured for vehicle traveling may be decreased, and the driving force that can be generated may be reduced.